The LCD (Liquid Crystal Display) has been broadly used in various applications in the daily life with the improvement and popularity of the digital network technology. Nowadays, the image quality of the LCD is nip and tuck with that of the CRT (Cathode Ray Tube) display. However, there are still some problems for the LCD needed to be improved and solved, such as the small viewing angle, the low contrast ratio, the long responding time, and the non-uniform displaying.
Many techniques are developed for obtaining a wider viewing angle of the LCD. Among so many WVA (Wide Viewing Angle) techniques, for example, the MVA (Multi-domain Vertical Alignment) technique is the technique utilizing the properties of the non-identical directions in arrangements and rotations of the LC (Liquid Crystal) molecules to increase the viewing angle and shorten the responding time of the LCD.
Please refer to FIG. 1, which illustrates the known MVA technique well. When a voltage is applied to the LCD by a transistor, the LC molecules will be promoted to align in various directions by the surface prominence, such as bumps and protrusions. The working principle adapted for the known MVA technique is described in the following.
As shown in FIG. 1, a known LCD 1′ is mainly formed by an upper substrate 11′ and a lower substrate 13′. The LC layer 12′ is located therebetween. A first electrode 111′ is located between the upper substrate 11′ and a second electrode 131′ is located between the lower substrate 13′ and the LC layer 12′. The first electrode 111′ and the second electrode 131′ further respectively have a plurality of surface prominences located thereon, such as 112′ and 132′. The surface prominences 112′ and 132′ are able to affect the electric field applied thereon and each pixel of the LCD is thus divided into multiple domains.
The MVA technique carries out a shorter response time for signals, a wider viewing angle and a higher contrast. Furthermore, this technique is always helpful to improve the displaying uniformity and is able to provide a more perfect image quality for the LCD 1′. However, the difficulty of manufacturing the surface prominences (e.g. 112′ and 132′) on the electrodes is hardly overcome and much time-consuming, which results in a higher product cost for the LCD 1′.
The BBVA (Biased Bending Vertical Alignment) technique, another application in the WVA techniques, relates to adjusting the arrangements and rotates of the LC molecules in various directions by means of the electricity. Please refer to FIG. 2, which illustrates the structure of a known BBVA LCD and the working principle thereof. The LCD 2′ is constructed of an upper substrate 21′ and a lower substrate 23′, which respectively have a first electrode 211′ and a second electrode 231′. Additionally, the second electrode 231′ (i.e. the pixel electrode for the BBVA LCD 2′) further has plural holes 232′ thereon. The third electrode 233′ (i.e. the biased electrode especially for the BBVA LCD 2′) is located between the second electrode 231′ and the lower substrate 23′ and corresponding to the hole 232′. The LC molecules 22′ will be aligned and rotated in various directions due to the functions of the second electrode 231′ and the third electrode 233′. The effect of multi-domain division is hence achieved. Furthermore, the complicated manufacturing process of the surface prominence for the conventional MVA technique is never needed and the BBVA technique has more potential in applications therefore.
However, some problems still exist in the BBVA LCD application, e.g. the disclination of the LC molecules. The LC molecules 22′ will be aligned disclinatedly on the fringe of the overlapping field of the second electrode 231′ and the third electrode 233′. Disclinations of the LC molecules result in delaying the responding time and the twinklingly displaying for the BBVA LCD.
Please refer to FIG. 3, which illustrates the structure of electrodes in another known BBVA LCD. The second electrode 31′ (i.e. the pixel electrode) in the BBVA LCD has a plurality of apertures 311′, and the third electrode 32′ (i.e. the biased electrode) is positioned under the second electrode 31′ and opposite to the apertures 311′, which enables the BBVA LCD to have a shorter response time and the twinkling phenomenon in displaying can be inhibited. However, for preventing the LC molecules from the disclination, the voltage difference between the voltage applied on the second electrode 31′ and that applied on the third electrode 32′ would be high, which is another drawback needed to be overcome.
Please refer FIG. 4, for example, when the voltage of the first electrode (not shown) is 0V, a voltage of 7V and a voltage of 10V are respectively applied on the second electrode 31′ and the third electrode 32′, and the voltage difference therebetween is still not enough to prevent the existence of the disclination 331′ in the BBVA LCD. In other words, a higher voltage difference is necessary to be applied for eliminating the disclination 331′, which would be a limiting factor in the application and the product cost, however.
Based on the above discussions, it is clear that for improving the practicability and utility of the BBVA technique, problems of the LC molecule disclinations have to be solved in combination of lowering the voltages respectively applied on the bias electrode. In order to overcome the drawbacks in the prior art, an improved BBVA LCD is provided in the present invention.